Currently available methods of labelling macromolecules, and in particular biological macromolecules such as fibrin, may be influenced by the chemistry of the detectable marker with which the macromolecule is to be labelled. In particular, subsidiary effects resulting from the chemistry of the marker and the macromolecule being labelled may cause artifactual results. Ideally, the marker should have no influence on the macromolecule to be labelled.
It is extremely important in many applications to achieve accurate and specific labelling of macromolecules such as fibrin. For example, areas of clot detection in pathological states such as deep venous thrombosis, thrombophlebitis, and lesions in the vasculature generally require accurate and specific labelling, particularly as morbidity and mortality caused by intravenous clots is an increasingly prominent public health issue throughout the world.
Currently, there are several methods of detecting intravenous clots. For example, use is commonly made of two imaging agents which have similar capabilities for identifying such clots. These include fibrinogen labelled with 125I and a labelled 3B6 monoclonal antibody. The 125I labelled fibrinogen has, however, been found to be nonspecific and capable of giving false positive results.
“Technegas” is an agent whose original purpose was to perform high quality diagnostic imaging of airways of the lungs to facilitate the detection of blood clots. This was primarily used in conjunction with a blood flow agent for the differential diagnosis of blood clots. The agent “Technegas” consists of a plurality of discrete particles, each comprising a plurality of coating layers of carbon (varying between two and ten atoms in thickness) which completely enclose a minute crystal of 99mTc metal. The particles are stable inert hydrophobic particles having a cross-sectional dimension of between 5 and 30 nm and a thickness of about 3 nm. The “Technegas” production process creates millions of these particles suspended in a carrier gas of argon. In this form the particles may be inhaled directly and become deposited in the alveolar spaces of the lung. From this distribution can be created three-dimensional maps of the airways by detecting the gamma ray signal generated by the decay of the Tc from the excited to the ground state (99mTc→99Tc).
The possibility of using the particles in liquid suspension as a “nanocolloid” suitable for biological and industrial applications has now been investigated. In particular, investigations have been made to find methods of extracting “Technegas” particles from argon gas directly into a physiological solution such as, for example, saline solution.